(1) Field of the Invention
This invention relates to telephone communications, and more particularly to the identification and analysis of status and condition of the pairs of wire in a telephone cable.
Applicant furthermore designates a computer designer as a person having ordinary skill in the art inasmuch as this analysis is done by computer. Therefore, this application is written so that a computer designer would be able to manufacture the unit and explain to telephone maintenance personnel the use thereof.
(2) Description of the Prior Art
The normal telephone system includes a central office where the telephone switching occurs, and from the central office extend many cables, each having many pairs of wire. These pairs of wire will extend to another central office or into the field to either individual telephones in homes or telephones or other equipment in businesses. Before this invention, it had been common practice in the telephone systems to inspect the different pairs of wire in a telephone cable in the field.
Between the central office and the phone there are numerous junction boxes or the like. Before this invention, it was known that a certain analysis could be made at these junction boxes or any point the pair was accessible. The two wires of a pair are designated in the phone system as the ring and tip. One wire being the ring and one wire being the tip of each pair. It was known that various tests could be made; e.g., the voltage determined between the ring and tip, the ring and ground, and tip and ground. Also, in the absence of voltage, the resistance from ring to tip, ring to ground, and tip to ground could be determined. It was known that if these measurements were of certain value, it could be determined whether the pair was a "plain old telephone service" (herein called POTS)" and also from this whether the pair was an idle or a busy POTS.
Typically in the standard telephone system used in the United States, the POTS will have a voltage from ring to ground of about -50 volts, plus or minus 5 volts, and the tip will have a low resistance from tip to ground. I.e., it will have a typical tip to ground resistance of 1,000 ohms, when idle. When busy, the tip to ground will have a voltage of approximately -15 volts, plus or minus 9 volts.
Also, some indication was obtained if other equipment were connected on the pair, e.g., a pay phone or an alarm system.
Furthermore, equipment existed before this invention to measure the capacitance. The capacitance between the ring and tip could be measured. The standard wire in common use would have a certain capacitance of per thousand feet. Therefore, by measuring the capacitance between ring and tip, a measurement could be obtained of the total length of wire. if the capacitance from ring to ground did not equal the capacitance from tip to ground, this difference indicated that the pair was unbalanced.
Furthermore, it was known, because of certain external conditions, the voltage of the wires would vary on an instantaneous basis. Therefore, for accuracy, no reading should be instantaneous but the average of multiple readings. Of course with structural devices, such as a volt meter having a needle indicating the volts, the inertia of the physical parts act as to average the reading inasmuch as the change in voltage would be so rapid that the needle could not physically move, but because of inertia, would average the instantaneous values.
Furthermore, many, if not most, central offices are equipped with "automatic number identification equipment" (called ANI herein) and also, many of the central offices ae equipped with "automatic number announcement converters" (called ANAC herein). Therefore, this equipment permitted a person at a terminal box in the field to dial on a pair a particular entry number or coded message request or ANI request (ANIR herein). In response to this ANIR dialed from the field, the ANI would identify the number of the line and the ANAC would announce by voice synthesizer, the telephone number of that line.